Influence of Microstructure on the Corrosion Behavior of V-N-Cr Microalloyed Added Weathering Steels

Abstract

The impact of microstructure on the corrosion behavior of V-N-Cr microalloyed added weathering steels was investigated using various materials characterization techniques including optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA), potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS). These methods were employed to analyze the corroded layer, identify principal phases, and observe morphology. The microstructure of V-N-Cr microalloyed added weathering steel, which includes ferrite, granular bainite, acicular ferrite, and a small amount of fine pearlite after cooling at 590 °C. Polygonal ferrite, lamellar bainite, granular bainite, and some acicular ferrite were present after cooling at 420 °C. Results from wet/dry cyclic corrosion tests showed that Type 2 V-N-Cr microalloyed added weathering steel (cooled at 590 °C) exhibited greater corrosion resistance compared to Type 1 steel (cooled at 420 °C), forming a protective barrier layer that effectively stabilizes the corrosion rate. The fine precipitates contributed to the development of a thicker, denser, and more stable corroded layer in the steel under investigation. Exposure of V-N-Cr microalloyed added weathering steels to a simulated industrial atmosphere resulted in the formation of various corrosion products, predominantly iron-rich oxides such as γ-FeOOH (lepidocrocite), α-FeOOH (goethite), Fe₃O₄ and Fe₂O₃ (hematite).